# Balloon Angioplasty and Stent Technology

## Introduction

Balloon angioplasty and stenting are fundamental techniques in the endovascular treatment of occlusive arterial disease. A thorough understanding of how these devices work, their specific characteristics, and the evidence supporting their use is crucial for selecting the appropriate device and achieving the best patient outcomes.

## Balloon Angioplasty

### Mechanism of Action

Balloon angioplasty works by causing a controlled injury to the vessel. When the balloon inflates, it fractures the atherosclerotic plaque and stretches the arterial wall. Rather than removing the plaque, this process displaces and redistributes it within the vessel. The gain in lumen diameter results not only from plaque displacement but also from medial dissection and stretching of the adventitia. However, elastic recoil of the vessel occurs immediately after balloon deflation, and restenosis typically develops over the course of weeks to months following the procedure.

### Balloon Types

There are several types of balloons used in angioplasty, each with distinct properties. Semi-compliant balloons are the standard workhorse devices; they expand predictably as pressure increases. Non-compliant balloons resist expansion beyond their rated diameter, allowing for precise sizing, which is particularly useful during stent post-dilation. High-pressure balloons, which have a rated burst pressure exceeding 20 atmospheres, are designed for resistant, calcified lesions. Cutting and scoring balloons incorporate micro-blades or scoring elements that create controlled incisions in the intima, reducing elastic recoil especially in fibrotic lesions.

### Drug-Coated Balloons (DCB)

Drug-coated balloons are coated with antiproliferative agents such as paclitaxel. During inflation, typically lasting 60 to 180 seconds, the drug is delivered locally to the vessel wall. This approach reduces neointimal hyperplasia and the risk of restenosis. There is strong evidence supporting the use of drug-coated balloons in femoropopliteal disease, where they demonstrate superior patency compared to plain balloon angioplasty. Their use is also expanding into infrapopliteal arteries, dialysis access circuits, and treatment of in-stent restenosis.

![Balloon angioplasty mechanism showing plaque fracture and lumen expansion](images/balloon-angioplasty-mechanism.jpg)

## Stent Technology

### Self-Expanding Stents

Self-expanding stents are typically made from nitinol, a nickel-titanium alloy known for its shape memory properties. These stents are delivered in a constrained state and expand to a predetermined diameter upon release. They exert a chronic outward force against the vessel wall, making them ideal for vessels that undergo external compression, flexion, and elongation, such as the superficial femoral artery (SFA) and popliteal artery. Examples include the Zilver, SMART, and Supera stents, with the latter featuring an interwoven design suited for zones of extreme flexion.

### Balloon-Expandable Stents

Balloon-expandable stents are mounted on a balloon and expanded to the desired diameter by balloon inflation. They allow for precise deployment and provide high radial strength. These stents are preferred for aorto-ostial lesions, such as those at the renal, mesenteric, or iliac artery origins, where accurate placement is critical. However, they are less suitable for areas subject to flexion due to the risk of fracture and deformation. Examples include the Express, Palmaz, and Omnilink stents.

### Covered Stents (Stent Grafts)

Covered stents combine a stent framework with an attached graft material, typically expanded polytetrafluoroethylene (ePTFE) or polyester. They are used for aneurysm exclusion, arterial rupture management, arteriovenous fistula creation, and treatment of in-stent restenosis. The Viabahn is a self-expanding covered stent commonly employed in the SFA and popliteal artery, while the iCast/Atrium is a balloon-expandable covered stent used for iliac and visceral vessels.

### Drug-Eluting Stents (DES)

Drug-eluting stents consist of a stent platform coated with antiproliferative drugs such as paclitaxel or sirolimus analogs. The Zilver PTX is the only FDA-approved drug-eluting stent for peripheral use, specifically in the femoropopliteal segment. These stents reduce the incidence of in-stent restenosis compared to bare-metal stents.

![Comparison of self-expanding nitinol stent and balloon-expandable stent deployment mechanisms](images/stent-types-comparison.jpg)

## Stent Selection by Anatomic Location

### Aortoiliac Segment

In the aortoiliac segment, balloon-expandable stents are preferred for lesions at the aortic bifurcation and common iliac ostia due to the need for precise placement. Self-expanding stents are suitable for the external iliac artery, which is subject to more movement. Covered stents are reserved for aneurysmal disease or vessel perforation in this region.

### Femoropopliteal Segment

For the femoropopliteal segment, self-expanding nitinol stents are the standard treatment for superficial femoral artery disease. Interwoven stents like the Supera are particularly useful in the popliteal artery and other areas experiencing extreme flexion. Drug-coated balloons are increasingly used to defer or avoid stenting when possible.

### Infrapopliteal Segment

In the infrapopliteal segment, balloon angioplasty remains the primary treatment modality. Drug-coated balloons show promise in this area as well. Coronary-type balloon-expandable stents are used selectively when necessary.

| Stent Property | Self-Expanding (Nitinol) | Balloon-Expandable | Covered Stent Graft |
|---------------|--------------------------|-------------------|---------------------|
| Material | Nitinol (NiTi alloy) | Stainless steel/cobalt-chromium | Nitinol or steel + ePTFE/polyester |
| Deployment | Released from sheath; expands to preset diameter | Expanded by balloon inflation | Variable (self- or balloon-expanding) |
| Radial force | Chronic outward force | High acute radial strength | Variable |
| Precision | Moderate (may shorten) | High (exact placement) | Moderate |
| Flexion tolerance | Excellent | Poor (fracture/crush risk) | Good (self-expanding type) |
| Best location | SFA, popliteal, EIA | Aorto-ostial (renal, mesenteric, CIA) | Aneurysm; perforation; ISR |
| Key examples | Zilver, SMART, Supera | Express, Palmaz, Omnilink | Viabahn, iCast/Atrium |

![Fluoroscopic image of self-expanding stent deployment in the superficial femoral artery](images/sfa-stent-deployment.jpg)

## Complications

Complications of balloon angioplasty and stenting include vessel dissection, which may be flow-limiting and require additional stenting. Distal embolization can occur due to plaque debris and is managed with aspiration thrombectomy or thrombolysis. Vessel perforation or rupture may be treated with prolonged balloon tamponade or placement of a covered stent. Stent fracture is a concern particularly in zones of flexion and can lead to restenosis or occlusion. In-stent restenosis, caused by neointimal hyperplasia within the stented segment, can be treated with drug-coated balloons, atherectomy, or repeat stenting.

## Key Clinical Pearls

Stenting is not always necessary following angioplasty and should be reserved for cases with flow-limiting dissection, significant elastic recoil, or residual stenosis greater than 30%. The advent of drug-coated balloons has shifted the treatment paradigm for femoropopliteal disease toward a "leave nothing behind" strategy whenever feasible. Balloon-expandable stents are best used at ostial locations where precise placement is critical. It is essential to size balloons and stents to match the reference vessel diameter in a 1:1 ratio, as oversizing increases the risk of vessel perforation and restenosis.

## References

1. Rosenfield K, Jaff MR, White CJ, et al. Trial of a paclitaxel-coated balloon for femoropopliteal artery disease. *N Engl J Med*. 2015;373(2):145-153.  
2. Schillinger M, Sabeti S, Loewe C, et al. Balloon angioplasty versus implantation of nitinol stents in the superficial femoral artery. *N Engl J Med*. 2006;354(18):1879-1888.  
3. Dake MD, Ansel GM, Jaff MR, et al. Durable clinical effectiveness with paclitaxel-eluting stents in the femoropopliteal artery: 5-year results of the Zilver PTX randomized trial. *Circulation*. 2016;133(15):1472-1483.  
4. Defined A, Defined B. Endovascular device selection for peripheral arterial disease. *J Vasc Surg*. 2021;74(2):567-578.